According to a closed cycle gas turbine of circulating a working fluid in a closed system by using an atomic reactor or the like for a heat source, an equipment capacity of a motor used for only operating to accelerate speed in starting, an electric apparatus SFC (Static Frequency Converter) or the like by using a generator as a motor is made to be as small as possible in order to achieve a reduction in plant construction cost.
Therefore, according to the closed cycle gas turbine, a speed is elevated to a rated revolution number in a state of reducing an amount of filling a working fluid in the closed system, for example, helium gas to a degree of circulating a fuel ball at inside of the atomic reactor by a flow of helium, and in a low temperature state.
In this way, a technology of reducing the amount of filling the working fluid in the closed system in starting has been proposed in a background art (refer to, for example, the Publication of Japanese Patent No. 3020853).
However, a temperature elevating rate of the atomic reactor is restricted, and therefore, even when the closed cycle gas turbine reaches the rated revolution number, the generator is used as the motor for some period of time. Therefore, there is continued an operation in a state in which a negative torque is loaded on a speed reduction gear or the like arranged between the closed cycle gas turbine and the generator.
Thereafter, the temperature of the working fluid flowing to the turbine is elevated by heat generation of the atomic reactor and a turbine output is increased. In the procedure, an axial output is changed from the negative output to the positive output and also a torque applied on the speed reduction gear or the like connecting the turbine and the generator is changed from the negative torque to a positive torque.
The speed reduction gear is prescribed with a necessary minimum torque for preventing a drawback of fretting or the like from being brought by shifting load sharing of the gear from a standard value by a self weight of the gear, or by shifting a contact position of teeth from a standard position.
Meanwhile, when the torque applied to the speed reduction gear or the like is changed from the negative torque to the positive torque as described above, there poses a problem that the torque necessarily becomes lower than the necessary minimum torque.
Further, since the temperature elevating rate of the atomic reactor is restricted, also a rate of increasing the torque applied to the speed reduction gear or the like is restricted and it is difficult to shorten a time period during which a torque becomes lower than the prescribed necessary minimum torque.